View-transmission system



Jan. 4, 1944. vV K, ZWORYKI 2,338,562

VIEW TRANSMISSION SYSTEM Original Filed May 1 1930 3 Sheets-Sheet l 480-77 INVENTOR llafor Wad/07 ATTORNE Jan, 4, 1944. v. K. ZWORYKIN 2,333,552

VIEW TRANSMISSION SYSTEM Original Filed May 1, 1950 3 Sheets-Sheet 2 R EL a as,

. I N V E N T O R V/dd/m/r K Z Wag/Hi1.

i BY

. I F. l ATTORN Jan. 4, 1944.

V. K. ZWORYKIN VIEW TRANSMISSION SYSTEM Original Filed May 1 1930 L] 5/5 M ME L 3 Sheets-Sheet 3 INVENTOR V/ad/mm/K Zwaryn'n.

AT ORN Patented Jan. 4, 1944 VIEW-TRANSMISSION SYSTEM Vladimir K.Zworykin, Forest Hills, N. Y., assignor to Westinghouse Electric &Manufacturing Company, a corporation of Pennsylvania Originalapplication May 1, 1930, Serial No. 448,834. Divided and thisapplication July 19, 1940, Serial No. 346,260

'7 Claims.

My invention relates to view-transmission systems and it has particularrelation to the lightsensitive devices used in such systems for thepurpose of deriving a fluctuating electric current representative of aview or a picture being transmitted.

This application is a division of my Patent No. 2,246,283 forView-transmission systems and assigned to the Westinghouse Electric 8:Manufacturing Company, Certain subject matter here disclosed is claimedin my Patent No. 2,141,059 and my applications Serial No. 242,505, filedNovember 26, 1938, and Serial No. 246,783, filed December 20, 1934.

In my copending application, Serial No. 376,117, filed July 5, 1929, andassigned to the Westinghouse Electric & Manufacturing Company, I havedisclosed a View-transmission system whereby a reproduction of amotion-picture film can be obtained, electrically, at a distance. Thetransmitting portion of the disclosed system comprises means for movinga film, longitudinally thereof, at a constant speed adjacent to a singlephotoelectric element and means whereby the film, in its passage, issubjected to the action of a scanning-ray of light that moves rapidlyfrom side to side across it.

In the operation of the system disclosed in my copending application,assuming that the film is advancing at the rate of 12 frames per secondbetween the scanning ray and the photo-electric element, that eachpicture frame is scanned by one hundred transverse lines and that eachscanning-line is divided into 100 linear pictureelements, it is apparentthat each of the pictureelements is exposed to the light during atimeinterval of only A of a second and is represented by aninfinitesimally small change in the output current from thephoto-electric element.

It would be highly desirable if the photoelectric element could beexposed for a longer time to the light passing through eachpictureelement but, if the scanning rate is made lower, the picturecould not be transmitted with suflicient rapidity to give rise to theillusion of motion at the receiving end.

Since a reduction in the scanning rate is impracticable, attention hasbeen paid to the development of photo-electric elements of greatersensitivity, and I have achieved a cer ain measure of success in thatdirection by the utilization of caesium oxide as a cathode material. Themost sensitive elements known at present, however, must be followed bymulti-stage amplifiers before their output currents, representingpictureelements, can be employed for controlling the transmission ofenergy to distant points.

Furthermore, the development of direct-view television systems, of thetype exemplified by the system set forth in my United States Patent No.

2,141,059, issued December 20, 1938, has been hampered by the high costof the light-sensitive cathode-ray tubes used therein, since the saidtubes do not lend themselves readily to factoryproduction methods.

It is, accordingly, an object of my invention to provide an improvedlight-sensitive cathode-ray tube that shall be inexpensive tomanufacture, and capable of being utilized in a view-transmission systemof either the direct or the indirect type.

Another object of my invention is to provide an improvedview-transmission system wherein a light-sensitive cathode-ray tube isemployed.

A light-sensitive cathode-ray tube, constructed according to a preferredembodiment of my invention, includes the following elements:

(A) A screen constituted by a plurality of minute light-sensitiveelements that are insulated from each other and from ground;

(B) A common anode disposed in spaced relation to the said elements;

(C) A common collector element mounted in spaced relation to saidlight-sensitive elements;

(D) Controllable means for producing a cathode ray; and

(E) Means for causing the ray to successively explore the rear surfaceof the screen.

When my improved cathode-ray tube is employed in a view-transmissionsystem, of either the direct or the indirect type, the view is focusedcontinuously upon the entire light-sensitive face of the screen and theindividual elements thereof, by reason of their distributed capacity toground, acquire positive charges proportional to the intensity andduration of the light.

The cathode-ray, as it explores the surface of the screen, also fallsupon the collector-element and causes an electronic flow thereover backto the source of the ray. The ray, however, each time it impinges uponone of the positively charged photo-elements, is robbed of sufiicientelectrons to neutralize the charge acquired by the element and,consequently, the steady flow of electrons is modulated, sequentially,to an extent proportional to the charges on the successive elements overwhich it sweeps.

In order that the modulation of the electronic stream may be utilized, Iinterpose a resistor in the circuit to interconnect thecollector-element and the cathode-ray source and connect the inputterminals of an amplifier across the resistor. The output current fromthe amplifier may be used to control the radiation of modulatedhighfrequency energy or the transmission of energy over metallicconductors to a plurality of viewreceiving stations.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of certain specificembodiments, when read in connection with the accompanying drawings,wherein Figure 1 is a diagrammatic View illustrating the usual way inwhich photo-electric elements are employed in television systems;

Fig. 2 is a simplified diagrammatic view of certain constituent elementsof an improved television system constructed according to onemodification of my invention;

Fig, 3 is a diagrammatic view of a complete television system,constructed and organized according to a preferred embodiment of myinvention, adapted to the purpose of transmittingfilmfacsimiles ordirect views.

Fig. 4 is a plan View, partly in section, of an actual light-sensitivecathode-ray tube of the type shown diagrammatically in Fig. 3;

Fig. 5 is an end view, partly in section, of the light-sensitiveelectrode-assembly of the tube shown in Fig. 4;

Fig. 6 is a sectional view of the electrodeassembly taken along a linecorresponding. to the line VIE-VI in Fig. 5;

Fig. '7 is a sectional View of the electrodeassembly taken along a linecorresponding to the line VIIVII in Fig. 5;

Figs. 8 and 9 are enlarged fragmentary front and rear views,respectively, of an electrodeassembly of alternative type;

Fig. 10 is a sectional view of the light-sensitiveelectrode-assemblyillustrated in Figs. 8 and 9, taken along a line corresponding to theline X-X of Fig, 8;

Figs. 11 and 12 are enlarged fragmentary front and rear views,respectively, of a light-sensitive screen of a further alternative type;

Figs. 13 and 14 are sectional views of the lightsensitive screenillustrated in Fig. 11; and

Fig. 15 is a simplified diagrammatic view of a view-transmission systemwherein a screen of the type shown in Figs. 11 to 14 is used.

In order that the principles underlying my invention may be thoroughlyunderstood, a brief rsum of the action of the photo-electric elementshown in my copending application, Serial No, 376,117, hereinbeforereferred to, will now be given, in connection with Fig. 1 of thedrawings.

The apparatus illustrated in Fig. 1 comprises a photo-electric element ihaving an. anode 3 and a cathode 5 that are interconnected through apotential-source 7 and a resistor 9, the resistor being disposed acrossthe input terminals of a suitable aperiodic amplifier H. A blockingcondenser I 3, preferably, is interposed between one terminal of theresistor and the amplifier, and. the negative terminal of thepotential-source 1 may be provided with a connection l5 to ground, ifdesired.

When the photo-electric element is exposed to the light that has passedthrough a movingfilm (not shown) from a transversely movingscanning-ray, or to light that is reflected from an object from asimilar scanning-ray, each pictureelement is represented by aninstantaneous minute change in the current flowing in the resistor 9,the amplitude of the current depending upon the intensity of the lightand the duration of exposure of the element to it. If, as previouslymentioned, a single frame of a film passes between the soanning-ray andthe photo-electric element in one second, and if the. frame. is.

scanned by one hundred lines, the photo-electric tube will be exposed tolight representing one ten-thousandth of the frame-area during the verysmall time-interval of fl of a second.

Obviously, the change in the output current from the photo-electricelement, for such a short exposure, is infinitesimal and, with the mostsensitive tubes now available, it is of the order of 3 l(l to 3 10amperes.

Since the limit in photo-electric element sensitivity seems to have beensubstantially reached, an increase, in element output current must beobtained through a radical modification of eretofore known scanningmethods. I propose, accordingly, to permit light from the view orpicture being televisioned to fall continuously upon a screenconstituted by a plurality of small photo-electric elements, to store,in a plurality of individual reservoirs, the simultaneous outputcurrents from the several elements and to, thereafter, successivelydischarge the current-storage reservoirs, at the scanning frequency, inorder to derive readilyamp-lifiable currents representative. of thepicture-elements.

If the screen is to be used in television systems of the direct-viewtype, it maybe of such size that the entire View can be focused thereon;if it is to be used in film-facsimile systems, it may be constituted bya plurality of small photoelectric elements, linearly disposed, sincethe travel of the film through the apparatus takes the place of thevertical component of the motion of the. scanning-ray. Inasmuch asthestructure of the screen, insofar as the individual photo-electricelements thereof are concerned, isnot dependent upon the dimensionsthereof, it should. be clearly understood that Whenever the term screenis used hereinafter, either the linear or the planartype of screen isinferred,

except in those instances wherethe meaning of.

the term is clearly determinable from the context.

The theory underlying the manner of operation. of my improvedview-transmission system will beclearly understood from aconsiderationof Fig. 2 of the drawings wherein a singleone of theplurality of screen-elements is shown as aphoto-electric element i!having an anode l9 and a cathode 25-, the saidxelectrodes beinginterconnected through a potential source 23 and a condenser 25.

In the operation of the system exemplified by Fig, 2 of'the drawings,the light from an element of the view, whether it be an image directlyfocused upon the screen or from an illuminated,

ranslucent web, such as a motion-picture film, impinging continuouslyuponthe photo-electric tube I7, causes the upper plate of the condenser.

it to acquire a positive charge proportional to the intensity andduration of, the upon the tube. In order that the condenser may bedischarged periodically, a similar photo-. electric element 2'5 and aresistor fit-may be connected in shunt relation thereto, and a light,

source (not shown) may be so disposed with respect tothe secondphoto-electric element. as tov illuminate it intermittently at thescanning. rate.

Assuming that the tubes IT and 2?, in Fig. 2, are representative of asingle element of a screen of the linear type comprising any desirednumber of pairs of elements, one hundred, for example, and that amagnified image of a motionpicture film is caused to move across thescreen in a direction transverseto the linear extension thereof, it isevident thatthe effect of transverse \I scanning of the moving film by avibrating lightlight falling ray may be obtained by causing a ray oflight to traverse repeatedly the cathodes of the elements 21 instead ofthe film. In such event the discharge current from any individualelement, representing the light from a single picture-element, is asmany times greater than if the film were directly scanned by the lightray as the time of a single traverse of the discharge-ray across theentire screen is greater than the time required for the direct scanningof the said picture-element. In other Words, by causing the light tostay on the individual photo-electric element in my improved screen onehundred times longer, I am enabled to obtain one hundred times moreoutput current, representative of a single pictureelement, than if asingle large photo-electric element were used.

By reason of manufacturing difiiculties, however, it is quite expensiveto provide each of the light-sensitive elements of the screen that areexposed to the view to be transmitted with an actual storage condenserand an individual condenser-discharging photo-electric element. I havefound it expedient, therefore, to utilize the distributed capacity toground of the individual photo-electric elements as the storagereservoirs and to provide a source of cathode-rays for dissipating thecharges stored in the said distributed capacity.

A further modification of my invention, therefore, as illustrated inFig. 3 of the drawings, comprises an evacuated container 29 having aconical central portion 39, a circular front portion 3| and acylindrical rear portion 32. A screen, constituted by a plurality ofphoto-sensitive cathodes 33, that are insulated from each other and fromground, is disposed within the front portion 3| of the container. Eachcathode has a definite distributed capacity to ground which is indicatedin the drawings by the condensers 34 shown in dotted lines. A commonanode 35 is provided for all of the photo-sensitive cathodes, andpotential is supplied thereto from a common source 31..

Each individual cathode 33 has a conductive portion 39 which extendsrearwardly of the screen, and a common collector-element 4| is disposedin spaced relation to all of the said portions 39 and insulatedtherefrom. The collector element is connected to the negative terminalof the potential source 31 through a resistor 43. A conductor 45 extendsfrom the negative terminal of the potential source 37 to ground. Theends of the resistor are connected, respectively, to the input terminalsof an amplifier 46 that may be of any suitable type.

A controllable source of cathode-rays, or an electron gun, is supportedfrom a press 4! disposed within the cylindrical rear portion 32 of thecontainer 36. The gun comprises a thermionic cathode constituted by ametallic thimble 48 having an active end portion 19, a cylindrical gridthat surrounds the cathode and a cylindrical anode 53 disposed coaxiallywith the grid. The cathode is provided with a heater 54, preferablyconstituted by a filamentary resistor imbedded in vitreous material orclay (not shown). The thimble, grid and anode are preferably fabricatedfrom non-magnetic material such as tantalum, or a 50% nickel-copperalloy.

Any suitable potential source 55 may be connected across the terminalsof the heater 54, and a single high potential source 51, the positivetercathode.

minal of which is connected to ground, is provided for biasing the anode53 and a focusing In order that the cathode-ray shall be caused torepeatedly sweep over the backward-extending portions 39 of thephoto-sensitive cathodes 33 and the collector-element 4|, a plurality ofdeflector members, such as plates BI and 63 or a plurality of coils (notshown) are provided.

A control-condenser 65 is connected in shunt relation to the deflectingplates, and charging means for the condenser, constituted by arectifying device 61, a resistor 69 and a high-potential source II, areprovided. The time required by the ray to travel from one end of therear surface of the screen to the other end, under the influence of thefield between the plates GI and 63, is determined by the rate at whichthe charge builds up on the condenser, which rate is dependent upon therelative magnitudes of the condenser 65 and the resistor 39.

Since it is necessary to cause the ray to quickly return to its startingpoint at the end of each traverse, a short-circuiting device isconnected in shunt relation to the control-condenser '65. Theshort-circuiting device, preferably takes the form of a thermionictriode 12 having an input electrode T3 normally biased negatively to thecut-off point by a source 75 of biasing potential and provided withmeans, such as a 480 cycle oscillator TI, for periodically overcomingthe grid-biasing potential to thereby permit the short-circuiting deviceto become conductive.

It is highly desirable that the cathode-ray shall repeatedly traversethe screen in one direction only and that it shall be diverted therefromduring the return intervals. For that purpose, the primary winding 18 ofa transformer 19 is connected between the anode of the short-circuitingtube and one terminal of the condenser 65, and the secondary winding Bilof the transformer together with a source SI of negative biasingpotential, is connected between the grid 5i of the electron gun and thecathode-thimble 48. The transformer-winding connections are so chosenthat, upon the flow of the condenser-discharge current in theshort-circuiting tube 12, sufficient additional negative potential isapplied to the grid 5| of the electron gun, with respect to the cathode48 thereof, to substantially cut off all electronflow from the saidcathode. The cathode-ray, therefore, is of normal intensity as ittraverses the screen in one direction during the charging of thecondenser 85, and is of very low intensity as it returns to the initialpoint preparatory to the next succeeding swing.

From the foregoing it will be seen that, in the embodiment of my presentinvention, wherein a motion-picture film is televisioned and moved atthe proper rate with respect to the path traversed by the cathode ray,this path remaining substantially in a given plane perpendicular to thescreen onto which the film is projected and the cathode ray deflectedback and forth repeatedly across the image on the screen, that is, firstin one direction along said path from an initial point and then back inthe opposite or return direction to the initial point, the result willbe a scanning of the image along a saw-tooth, the height or altitude ofthe teeth being determined by the amplitude or degree of deflection ofthe ray by the plates BI and 63, the pitch of the teeth or distancebetween adjacent tooth-points being determined by the rate of movementor travel of the film- When it s do sired to employ the action justdescribed, which I refer to as saw-tooth scanning, the adjustments inthe system are such that the intensity of. the cathode ray is normal asit traverse the screen in one direction but is of relatively lowintensity as it returns in the opposite direction to that side of thescreen from whence it started the preceding effective scanning movement.

When, however, the adjustments in the. system are such that the electronflow from" the cathode is entirely or substantially entirely cut oilupon and during discharge of the condenser 55, the result is that thecathode ray is put out at the beginning of and during the returnmovement back to that side of the screen from whence it will start thenext effective scanning movement. The result of such action is that thescreen is scanned by parallel lines, each starting at the same side ofthe screen and ending abruptly at the other side, these lines being madeone after the other in rapid succession. at a rate determined by therate of charging and discharging of con denser This method or manner ofscanning, I refer to as unilateral scanning.

In the operation of my improved system, when motion-picture films or thelike are televisioned, an enlarged image of a minor longitudinal portionof a moving film is cast upon the cathode screen by an appropriateoptical system (not shown) in alignment with the light-sensitiveelements thereof, as indicated by a plurality of arrows $3 in Fig. 3which represent instantaneous light-intensities. Each individual cathodeemits electrons under the influence of the light impinging upon it andacquires a positive charge, with respect to ground, proportional to theintensity and duration of the light from a single minor view element.

Were it not for the positive charges acquired by the screen-elements,the moving cathode-ray falling upon the collector element 4-! would giverise to a steady unidirectional electron flow over the resistor and,through the grounded co-nductor it, back to the cathode of the electrongun. By reason of the said positive charges, however, the cathode-ray issuccessively robbed of sufficientelectrons for the neutralizationthereof, as it traverses the conductive extensions of thephoto-sensitive cathodes, and the electronic flow through the resistorl? consequently is modulated to an equivalent extent.

Each time, therefore, that the cathode-ray sweeps with full strengthfrom one end of the screen to the other, the current through theresistor is ceased to pulsate and the pulsations are amplified theamplifier it for subsequent action of any suitable radio or wire transm'ter. It should be clearly understood in this connection that the outputcurrent from each screen-element 33, since it is equivalent to thecharging current to the distributed capacity to ground 3 iassociatedwith the said element during the entire time that the ray requires toreturn ther to from the last preceding contact therewith, is very muchgreater than when only a single photo-electric element is used, astaught by the prior art.

My improved cathode-ray tube, having a linear screen, also be employed,without material modification, for the direct televisioning ofilluminated animate or inanimate objects. When the system is organized for direct television an im age of the object is formed, by appropriateoptical means, in the plane of the photo sensitive cathodes constitutingthe screen, and the said image, through the use of a rotatin polygonalmirror, or'a similar device, is causedto repeatedly move over thescreenin a direction perpendicular to the linear extension thereof, thussimulating the movement of a him. For satisfactory results, the rateofmovement of the image should be such that at least twelve images persecond are completely explored by the screen.

An actual cathode-ray device, except that the relative dimensions of theparts thereof may be widely departed from in practice, of the type shownonly diagrammatically in Fig. 3, is illustrated in Figs. i, 5, 6 and '7,wherein the parts analogous to those of the tube shown in Fig. 3 aresimilarly designated.

Ashereinbefore described, the device comprises an evacuated container 29having a conical central portion 36, a circular front portion 3| and acylindrical rear portion 32 wherein the electron gun is disposed.

The light-sensitive electrode-assembly is mounted in the circular endportion 31 of the device and is constituted by a stack of interleavedmetallic electrodes and glass insulators 8.1 that are compressed betweentwo lavite endplates 89 by a. plurality of tie-rods 9|.

Each end of each of the insulators 8! is shaped to conform to thetie-rod adjacent thereto, in order that the insulators shall beprevented from twisting, as indicated in Figs. 6 and '7.

Each of the metallic electrodes has a front bent-over silver-platedportion that carries one of the small photo-sensitive cathodes 33 and arearwardly extending portion corresponding to the element 39 shown inFig. 3. Each portion 39 has an opening 92 extending therethrough toaccommodate the collector-element 4i that is common to all of theportions 39 and is supported from the end-plates 89.

The common anode 35 is also supported from the end-plates 89 and isdisposed closely adjacent to the cathodes 33.

The entire electrode assembly is supported by a plurality of rods 93that are imbedded in a plurality of presses 95 and 91 that extendinwardly from the periphery of the circular portion 3! of the tube. Theanode 35, the collector 4i and the tie rods 9| are, respectively,provided with leads 9%}, I all and [t3 that extend through the pressesto the exterior of the tube.

It will be noted from an inspection of Fig. 5 that the main tie rods 6!are electrically connected together and are indicated as being connectedto ground. By reason of this fact, therefore, each of thephoto-electrically active cathodes has a definite capacity to ground, asindicated by the condensers 34 shown in dotted line in Fig. 3 of thedrawings.

In the process of manufacturingmy improved cathode-ray device, after theelectron gun and the unsensitized screen-electrode assembly are mountedwithin the container, the silver-plated surfaces of thecathode-electrodes are oxidized to a definite degree by causing anelectric discharge to occur between two electrodes, such as the commonanode 35 and the common collector ii, in an atmosphere of oxygen.

The device is next thoroughly evacuated and the electrodes degasified bymethods well known to those skilled in the art. A nickel receptacle(positioned within the container adjacent to the silvered portions ofthe cathode-electrodes) that contains a material, such as a mixture ofcaesium dichromate and silicon, which will free caesium when heated, isheated by high frequency currents induced therein by an internal coil.This frees the caesium and it is deposited upon the ends of theelectrodes carrying the oxidized silver coating.

The device is then heated to a temperature of between 150 and 200centigrade and maintained thereat until the silver-oxide-coated portionsof the electrodes assume a rusty yellow color indicative of thecompletion of the sensitizing process. The color is probably caused bythe formation of sub-oxides of caesium.

The device is next given a final exhaust to remove all residual gasesand is'sealed off from the pump.

It is also feasible to construct an electrode assembly of either thelinear or planar type by the fusion together of a plurality of smallcylinders of insulating material, the axes of which are parallel andperpendicular to the front and rear surfaces of the screen. Such screenis exemplified in Figs. 8, 9 and 10 of the drawings.

Referring specifically to Figs. 8, 9 and 10, a plurality of glasscylinders I are fused together to constitute an insulating supportsomewhat analogous, in superficial appearance to an empty honey-comb.One face of the composite insulator is provided with a metallic coatingI01 by spraying from a Schoop-pistol or by an electroplating. A silverrivet I09 extends through each of the small glass cylinders, the ends ofeach rivet being split and opened up slightly to prevent them fromloosening. The split ends of the rivets are in capacitive relation tothe conductive layer I 01 which corresponds in function to the collectorelement 4| shown in Figs. 3 and 4.

The rounded surfaces of the rivet-heads are provided with layers ofphoto-electrically active material (not shown), such as caesium-oxide,and each rivet is thoroughly insulated from the neighboring rivets bythe glass cylinders.

When a screen of the type illustrated in Figs. 8, 9 and 10 is mounted ina cathode-ray tube of the type hereinbefore described, a common anodeelement, analogous to the element 35 in Figs. 3 and 4, is disposed inspaced relation to the photosensitive rivet heads.

Instead of constructing the light-sensitive screen by assemblingtogether a plurality of physically separate photo-tubes, it also lieswithin the scope of my invention to form the said tubes in situ upon asingle supporting member.

Referring specifically to Figs. 11, 12, 13 and 14 of the drawings, thesupporting member, instead of being constituted by a plurality of glasscylinders, may be a metallic plate II3 having a plurality of openingsII5 extending therethrough,

. type and a great number of separated spots H9 of metallic silver aredepos ted thereon. The

proper positioning of the silver spots may be assured by interposing aperforated plate between the gun and the prepared sheet or they may bedeposited by any other convenient method such as sputtering,evaporation, or electrolytic deposition. Irrespective of the methodemployed, however, great precaution should be taken to ensure that thesilver spots are each electrically disconnected from the others since itis upon their complete insulation that satisfactory operation depends.

The plate carrying the silver spots is next subjected to an oxidizingprocess to form a coating of silver oxide on each of the said spots. Theoxidation of the silver spots may be satisfactorily accomplished bysubjecting the plate to an electric discharge in an atmosphere ofoxygen.

The final step in the process consists in heating the plate in thepresence of vaporized caesium to render each of the silver spotsphoto-sensitive. A sub-oxide of caesium is probably formed during theheating process but of this fact I am not quite certain.

The sensitive screen in its final form, therefore, comprises aconductive base, an insulating layer and. a large number of smallelectrically separated photo-sensitive spots carried upon the insulatinglayer, portions of the periphery of each .ray is caused to repeatedlytraverse the rear surface. thereof. When so used, a common anode,preferably a screen made from very fine wire having a relatively coarsemesh, is mounted in the tube closely adjacentto the light-sensitivespots, and a single conductive connection is made to the metallic platethat supports the said cathodes.

In order that the operation of the screen shall be understood when it issubjected to the simultaneous action of light and a cathode-ray, I haveillustrated, diagrammatically, in Fig. 15, the electrical circuit of asingle spot, to which figure attention should now be directed.

Referring specifically to Fig. 15, the condenser I23 represents thecapacity of a single photoelectric spot H9 with respect to th supportingplate II3. An anode I25, a resistor I21, a biasing battery I29 and asource I3I of cathode-- rays are common to all of the photo-electricspots.

When the spot is illuminated, a charging current flows into thecondenser I23, making the photo-electric element H9 positive withrespect to the conducting plate H3. The potential of the battery I29 andthe magnitude of the resistor I21 are so chosen that during at least iof a second, if illumination is maximum, the con-- 7 denser receives acharge C slightly less than its maximum capacity. If we denote thecharging current for each spot as I and the entire number of spots as N,then the total charging current, for illumination of the entirescreen'under maximum light conditions, is .NI amperes.

will be N times greater than that of the charging current thereto. :Suchbeing the case, the discharge current from a single element, for anevenly illuminated screen, will be equal to the total chargingcu-rrentfor the entire screen. -Inasmuch as the charging current may, forpractical purposes, be regarded .as devoid .offiuctu- :ations and-sincethe discharge current is constituted by-a succession of impulses atveryhigh frequency, it is vcomparatively,simple toiseparate' ,thedischarge currents-by properlyzdesigned-filters andto ,amplifythembefore impressing them upon a transmitting medium.

,It will, accordingly, be apparent that when a view, considered ascomprising N view-ele- ,ments, is, impressed uponthe sensitive-screen,the charging currents .to .the ,tiny. photo-cathodes,

covered by the view, during eof asecond, are proportional to .thevaryinglightand shade of the view-elements. -The, discharge currents,representative of successive view-.elements,when the photo-cathodes aresuccessively exposed to the ,scanningrray, .are equal to vthe chargingcurrents and, accordingly, are N timesgreater than in television systemsof the type-wherein one or more photo-electric cathodes are momentarilyexposed to light from successive view-elements.

'For IOOlingpictures, the photo-electric current issubstantial1yi10,'000 times as great as in conventional systems.

In the reception .of a televsioned view, I prefer to'utilize atube (notshown) having 'afluorescent screen overwhich a cathode-ray is caused tomove in synchronismwith the ray in the transmitting tube. The receivingtube is provided also with acontrol-electrode, interposed between .thesource of the rayand the screen, upon which electrode thereceivedimpulses, proportional to the instantaneous discharge currentsof the m1- nute photo-electric elements in the transmitting ,tube, areimpressed to control the intensity of the ray. Such tube forms no part.of the present invention, it beingobvious that other Well-knownreceiving devices may be utilized.

It will be apparent, from a careful consideration of the foregoingdescription of certain spe-, ciflc'embodimentsof .my invention, that alightsensitive cathode-ray tube constructed ,in accordance.therewitlihas .an apparent sensitivity, by reason of, thelarge outputcurrents obtainable therefrom, which is many times greater than thesensitivity of a single photo-electric element, no matter how large,when usedin television systems constructed and organized according tothe teachings of the prior art.

Furthermore, since scanning is accomplished byelectronic means devoid ofinertia, instead of by "mechanical means, .rny improved televisiontransmitter is noiseless and does not easily get out of adjustment.

In short,,my invention provides means whereby thedirect transmission ofviews of animate or inanimate objects canbeaccomplished and,accordingly, isan important-step forward in the art of television.

Although I have, shown and described several specific embodiments of myinventiomI amfully aware that many other modifications thereof arepossible.

' -I 'claim as myinvention:

1. A view-transmitting device comprising an image plate comprising 'aperforated conductive screen coatedwith insulating material andsupporting blocks of a conducting material, said blocks having aphoto-sensitive coatin thereon, means to scan the other side of saidblocks with an electron beam which emanates from a source connected tosaid screen.

2. A view-transmitting device comprising an image plate comprising aperforated metal screen coated with insulating material and supportingblocks of metal, said blocks having a photosensitive coating thereon,means .to scan said blocks with an electron beam 'which emanates from asource connected to said screen, and an anode connectedto said source.

8. An image plate for a view-transmitting apparatus, said platecomprising a perforated metal screen, having aninsulating coating oversubstantially its entire surface and having blocks of metal thereinextending within said perforations, said blocks having atphoto-sensitivecoating on one side only.

i. A view-transmitting.tdevice comprising an image plate comprisingaperforated sheet .of conducting material coated onsubstantially itsentire surface with a layer of insulation, each perforation having alayer of photo-sensitive metal adjacentthe major portion of itsperimeteron one side of said sheet, said photo-sensitive layers comprisingisolated areas.

.5. A view-transmitting device comprising an image plate comprising aperforated sheet of conducting material coated on substantially itsentire surface with alayer of insulation, each perforation having .alayer of photo-sensitive metal adjacent the. major portion ofitsperimeter on one side'of said sheet, said photo-sensitive layerscomprising isolated areas, means to scan the side of said sheet oppositeto said photosensitive areas with an electron beam emanating from asource which is connected to saidvsheet, ananode connected to saidsheet,and a collector electrode connected to said sheet.

6. A view-transmitting device comprising an image plate comprising aperforated sheet of conducting material coated on substantially itsentire surface with a layer of insulation, each perforation having alayer of photo-sensitive metal adjacent the major portion of itsperimeter on one side of said sheet, said photo-sensitivelayerscomprising isolated areas, means to scan the .side of said sheetopposite to .said photosensitive areas withan electron beam emanatingfroma source which is connected to said sheet, an anode connectedto said.sheet andpositioned on the side of said sheet which is scanned bysaidelectron beam, and a collector electrode connected to said sheet andpositioned on the side of said sheet opposite to that scanned by saidelectron beam.

7. A view-transmitting device comprising an image plate comprising aperforated sheet of conducting material coated on substantially itsentire surface with a layer of insulation, each perforation having alayer of photo-sensitive metal adjacent the major portion of itsperimeter on one side of said sheet, said photo-sensitive layerscomprising isolated areas, means to scan said plate with an electronbeam emanating from an electron source, and an anode and a collectorelectrode adjacent said plate and electrically connected to said source.

VLADIMIR K. ZWORYKIN.

